1. Field
One embodiment of the invention relates to a video transmission apparatus and a video transmission method, for example, having a function for transmitting video data to a display device by a wireless signal.
2. Description of the Related Art
In recent years, interface standards, such as Digital Visual Interface (DVI) and High-Definition Multimedia Interface (HDMI), have been used as interfaces for transmitting video data. The interfaces, such as DVI and HDMI, are used in order to transmit video data, such as a digital television signal, from a video transmission apparatus, such as a personal computer or a DVD (Digital Versatile Disc) player, to a display device-such as a TV set, a monitor or a projector.
In the interface such as DVI or HDMI, a hot plug detect signal is stipulated. The hot plug detect signal is a signal which indicates that the display device is connected to the video transmission apparatus and that the display device is able to display the video data. The hot plug detect signal is sent from the display device to the video transmission apparatus. Upon receiving the hot plug detect signal, the video transmission apparatus can start transmission of video data to the display device.
Jpn. Pat. Appln. KOKAI Publication No. 2006-203725 discloses an apparatus including an interface according to the HDMI standard. When the hot plug detect signal rises to a High level, this apparatus starts authentication with the display device and outputs an HDMI signal.
In the meantime, the interface standard such as DVI or HDMI, it is presupposed that the video transmission apparatus, which is called “source device”, and the display device, which is called “sink device”, are connected via a cable. However, since the cable connection restricts places where the video transmission apparatus and the display device are to be disposed, it is difficult to dispose the video transmission apparatus and the display device at arbitrary places.
If the interface, such as DVI or HDMI, is implemented by a wireless scheme, it becomes possible to dispose the video transmission apparatus and the display device at arbitrary places.
In order to wirelessly transmit video data from the video transmission apparatus to the display device, it is necessary to emulate a hot plug detect signal which indicates that the display device can display video data. Wireless communication, however, unlike wired communication, is affected by the peripheral environment and the distance between the video transmission apparatus and the display device. Thus, depending on the wireless connection environment, such a problem arises that the hot plug detect signal from the display device can or cannot be received by the video transmission apparatus, and the enable state and disable state of the hot plug detect signal are repeated. In this case, since the video transmission apparatus repeats the transmission start and transmission stop of the video data, such an unpleasant phenomenon for a user occurs that the screen image of the display device may flicker.
In the case of implementing the interface, such as DVI or HDMI, by a wireless scheme, it is necessary, therefore, to realize a novel function which can prevent flickering of a screen image due to instantaneous variation of the wireless connection environment.